Field of the Invention
The present invention relates to a radiation imaging apparatus, a radiation imaging method, and a program.
Description of the Related Art
As a radiation imaging apparatus, for example, an X-ray imaging apparatus using an FPD (Flat Panel Detector) has been commercialized. FPDs allow increases in area and reductions in thickness and weight. Portable X-ray imaging apparatuses using portable FPDs in cassette form are used for medical applications and the like.
Japanese Patent Laid-Open No. 2000-033082 discloses an image processing apparatus which recognizes an exposure field region of radiation, and sets a region of interest which is included in the recognized exposure field region and which includes the center point of the exposure field region. This apparatus then corrects the region of interest based on image data near the set region of interest. The apparatus decides image processing conditions based on the image data in the corrected region of interest, and performs image processing based on the decided image processing conditions.
Japanese Patent Laid-Open No. 2005-324058 discloses a radiation image processing apparatus which positions each of a plurality of chest radiation images indicating the respiratory dynamics of the chest of an object (a patient) and constituting a dynamic chest image, based on a predetermined anatomical region in each chest radiation image.
Japanese Patent Laid-Open No. 2004-056230 discloses a technique of estimating past and current rotational angles from past and current X-ray images as three-dimensional projection images, deriving a relational expression for obtaining one point f on the past image and a point g after deformation from the past image by using the obtained angles, and performing deformation for each depth. This reference discloses a method of obtaining the difference between the deformed past image and the current image. This method can position three-dimensional projection images even with back-and-forth tilting or rotation of a target.
According to Japanese Patent Laid-Open No. 2004-343176, when a user selects a mode of displaying only a shadow increase (disappearance) in the difference image generated by a difference processing unit, the difference image is subjected to tone conversion such that only the region where the shadow increases (disappears) has a brightness different from those of the remaining regions. This reference discloses an apparatus which displays the state of each shadow change individually as an image by displaying the tone-converted difference image on a display unit, thereby facilitating the observation of each shadow change. With this technique, when displaying a difference image, even if a plurality of shadow changes have occurred, the apparatus allows easy and reliable observation of each shadow change, and also allows easy and reliable determination to be performed in a follow-up.
Conventionally, surgical operations such as orthopedic operations have been performed by using surgical C-arms (moving image apparatuses). Some operations are performed by using portable radiation imaging apparatuses (e.g., portable X-ray imaging apparatuses) to which FPDs are connected in place of conventional surgical C-arms. The reason why a portable X-ray imaging apparatus is used in place of a surgical C-arm is that the apparatus provides the convenience of requiring a sensor to be placed near an operating table only when X-ray imaging is required. Another reason is that when a surgical C-arm is used, a sensor unit and a tube unit positioned near the operating table may interfere with excision and the like.
The portable radiation imaging apparatus has, however, a problem that the positional relationship between the sensor unit and the tube unit changes for every imaging operation. For this reason, it is necessary to perform image capture upon setting a wide radiation application range for a patient and to extract and display a region of interest from a captured image for every image capture. This extracting/displaying operation is generally performed several tens of times. That is, this operation is cumbersome. In addition, the extraction position of an assistant who performs the extracting operation varies. This may affect the determination made by a doctor.